JDK-8193445 Performance Test

[Dean Wookey]

Hi,

I was going to ask if it was possible to reopen JDK-8151756 (
https://bugs.openjdk.java.net/browse/JDK-8151756) since it was fixed but
reverted in JDK-8183100 (https://bugs.openjdk.java.net/browse/JDK-8183100)
after causing several regressions. I only noticed now that a followup bug
was created: JDK-8193445 which reopens the issue.

The code below demonstrates the problem where adding nodes to the scene
graph all at once performs exponentially slower than adding them one by
one. I get the following results with jfx11.0.1:

One by one: 138ms
All at once: 16704ms

I've made a potential fix, different to the one tried previously which
applies the css as if the nodes were being added one by one:
https://github.com/DeanWookey/openjdk-jfx/commit/65a1ed82bce262294f1969e9a12e1126ec8a1ec6

It passes the main tests, as well as the systemTest JDK8183100Test.java
from https://bugs.openjdk.java.net/browse/JDK-8193494.

This is probably not a suitable issue to work on for a first time
contributor, but perhaps I could work on a performance test if someone can
point me in the direction of existing performance tests?

Dean

package applycsstest;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

/**
 *
 * @author Dean
 */
public class ApplyCssTest extends Application {

    @Override
    public void start(Stage primaryStage) {
        System.out.println("One by one: " + addToSceneOneByOne() + "ms");
        System.out.println("All at once: " + addToSceneAllAtOnce() + "ms");
        Platform.exit();
    }

    public static void main(String[] args) {
        launch(args);
    }

    public long addToSceneOneByOne() {
        StackPane root = new StackPane();
        Scene scene = new Scene(root, 300, 250);

        long start = System.currentTimeMillis();
        StackPane firstChild = new StackPane();
        root.getChildren().add(firstChild); //add to the scene graph first
        addNodesOneByOne(1000, firstChild); //then add children one by one
        return System.currentTimeMillis() - start;
    }

    public long addToSceneAllAtOnce() {
        StackPane root = new StackPane();
        Scene scene = new Scene(root, 300, 250);

        long start = System.currentTimeMillis();
        StackPane firstChild = new StackPane();
        addNodesOneByOne(1000, firstChild); //build the node up, then
        root.getChildren().add(firstChild); //add to scene graph all at once
        return System.currentTimeMillis() - start;
    }

    public void addNodesOneByOne(int numToAdd, StackPane parent) {
        StackPane last = parent;
        for (int i = 0; i < numToAdd; i++) {
            StackPane curr = new StackPane();
            last.getChildren().add(curr);
            last = curr;
        }
    }
}